The invention relates generally to the field of image display technology, and in particular to processes for characterizing and driving flat panel displays such as Organic Light Emitting Diode (OLED) Displays.
In today""s digital infoimaging world, many images are previewed and manipulated on low-power, hand-held portable electronic flat panel displays. New display applications (i.e. cell phones, DVD, palm pilots, video games, GPS, etc.) impose greater design requirements and improved imaging performance than other imaging display devices used previously. Displays are intended to provide a realistic representation of the images to the viewer, thus there is a need to correct display color and tonal responses to enhance the display image quality. The color and tonal enhancement must be implemented in the display""s imaging chain.
Flat panel displays such as OLED displays have the potential for providing superior performance in brightness and color resolution, wide viewing angle, low power consumption, and compact and robust physical characteristics. However, unlike CRTs, these flat panel displays have a fixed white point and a chromatic neutral response that result from the manufacturing process, and are not adjustable. Variations in the manufacturing process result in variations in the white point and chromatic neutral and therefore unwanted variations in display color reproduction. With manufacturing processing variability and the need to increase yield to lower costs, it becomes imperative to develop robust and easy to implement color characterization and display driving techniques that accommodate for manufacturing variations.
There is a need therefore for an improved method of calibrating and driving flat panel displays.
The need is met according to the present invention by providing a method of calibrating a flat panel, comprising the steps of:
a) providing a flat panel display having an overall and individual channel adjustment for both gain and offset, and an adjustment to provide a white point for the display, the white point including color temperature, chromaticity and luminance level;
b) displaying a first target using a low level code value for each channel of the display;
c) sensing the luminance level of the displayed first target;
d) adjusting the gain of the display so that the sensed luminance level matches a first predetermined aim value representing a luminance level at least 3 decades lower than a maximum luminance level;
e) displaying a second target using intermediate code values for each channel of the display device;
f) sensing the luminance level and chromaticities of the displayed second target;
g) adjusting the individual channel offsets so that the luminance level matches a second predetermined aim value representing an intermediate luminance level and the chromaticities match a first set of predetermined chromaticities that represent a desired white point;
h) displaying a third target using maximum code values for each channel of the display;
i) sensing the luminance level and chromaticities of the displayed third target;
j) adjusting the individual channel gains so that the luminance level matches a third predetermined aim value representing a maximum luminance level and the chromaticities match the first set of predetermined chromaticities; and
k) repeating steps e) through j) a number of times until no further adjustment is required in step j).
According to a further aspect of the invention, the flat panel display is characterized by displaying further targets using intermediate code values for each channel of the display device; sensing the luminance level and chromaticities of the displayed further targets; and adjusting the individual channel offsets so that the luminance level matches the second predetermined aim value representing an intermediate luminance level and the chromaticities match a first set of predetermined chromaticities that represent a desired white point.
According to a still further aspect of the invention, a method for driving a color flat panel display with RGB code values, includes the steps of:
a) converting the RGB code values to aim RGB intensities;
b) transforming the aim RGB intensities to CIE XYZ values at a defined aim white point;
c) translating the CIE XYZ values to corresponding XYZ tristimulus values for the flat panel display white point;
d) transforming the corresponding XYZ tristimulus values to display RGB intensities;
e) converting the display RGB intensities to display drive RGB code values; and
f) applying the display drive RGB code values to the flat panel display.
The present invention has the advantage of correcting the multi-channel flat panel display""s neutral characteristic response to be achromatic. For example, it is capable of achieving achromatic responses for any given white point. It has the further advantage that the flat panel display driving algorithm can be easily implemented with software LUTs or with digital signal processing integrated circuit technology. The flat panel display characterization data can be stored onboard and changed if necessary, thus updating the driving algorithm for aging or customization. The present invention also has the advantage of modifying the multi-channel flat panel display""s color reproduction in order to achieve an aim. Using the present invention, an aim color reproduction can be achieved for any given white point. Future applications can be further advantaged using the neutral correction and color reproduction data to enhance a flat panel display""s visual appearance.